Looks like this may be UA policy. Here is a posting mainly about crappy service in Business but also mentions the non-stop from LAX going to a remote stand.
https://www.flyertalk.com/forum/34294506-post1.html. Probably saves them money somehow. In my case, you would think that the 2.f hour delay would have made them want to get the plane to a gate for its next flight, but apparently not.